Oxidation of isoeugenol to vanillin by the ¡°H₂O₂-vanadate-pyrazine-2-carboxylic acid¡± reagent

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• 作者：Elena V. Gusevskaya ; Luciano Menini ; Luciana A. Parreira ; Rafaela A. Mesquita ; Yuriy N. Kozlov ; Georgiy B. Shul¡¯pin
• 关键词：Hydrogen peroxide ; Oxidation ; Pyrazine-2-carboxylic acid ; Vanadium complexes ; Vanillin
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2012
• 出版时间：November, 2012
• 年：2012
• 卷：363-364
• 期：Complete
• 页码：140-147
• 全文大小：626 K

文摘

Isoeugenol [2-methoxy-4-(prop-1-en-1-yl)phenol; compound 1] can be oxidized to vanillin (4-hydroxy-3-methoxybenzaldehyde, compound 2) by H₂O₂ in the presence of the n-Bu₄NVO₃/pyrazine-2-carboxylic acid catalytic combination. A 50 % yield of 2 was attained in a 2-h reaction at 80 ¡ãC, with a turnover number being higher than 1200. Kinetics of the transformation of 1 into 2 have been studied. The results obtained indicate that the first step of the 1 activation is its interaction with a hydroxyl radical. Further transformations of the primary product formed in this step proceed via several routes, one of which leads to the formation of 2. It has been proposed that the interaction of vanadate with the first molecule of H₂O₂ gives a V(IV)-containing species and hydroperoxyl radical: ¡°V^V-OOH¡± ¡ú ¡°V^IV¡± + HOO. In the next step, the V(IV) complex reacts with the second molecule of H₂O₂ affording a hydroxyl radical and recovering a starting V(V)-containing species: ¡°V^IV¡± + H₂O₂ ¡ú ¡°V^V¡± + HO^? + HO. Then, the hydroxyl radical attacks a double bond in the substrate: HO + CHR¡äCHR¡å ¡ú CHR¡ä¨CCH(OH)R¡å. The carbon-centered radical formed in the latter step can rapidly capture a molecule of O₂ from the atmosphere: CHR¡ä¨CCH(OH)R¡å + O₂ ¡ú C(OO)HR¡ä¨CCH(OH)R¡å. Finally, a rupture of the CC bond gives rise to the formation of aldehyde 2.